The present invention relates to a drum-type wood chipper and more particularly to an apparatus and method for handling air within a drum-type wood chipper.
Drum-type wood chippers of the kind typically used to chip tree stems, tree limbs, branches, brush, wood scraps and other wood debris often include a housing having an internal chamber in which a chipper drum is supported for driven rotation. The drum carries a plurality of cutting knives spaced about its perimeter which, when wood debris is fed into the chamber, reduce the limbs and such to chips. The chips are discharged through an outlet in the chamber and transported by their momentum along a discharge chute for collection, typically in a chamber or bin, such as that provided on a towing vehicle used to transport the chipper.
As the type of wood and size of the chips can vary, it is not uncommon for some of the chips to be too light such that they have insufficient momentum to travel the length of the discharge chute and collect in the chamber. One proposed solution to the problem has been to add fan blades to the side of the drum in order to generate a flow of air in the chipping chamber to help carry the chips along. The flow of air, however, is difficult to control and in some cases an undesirable backflow develops wherein dust and light debris is discharged through the material inlet.
Another proposal has been to equip such chippers with a discharge fan external to the housing that is driven off the drum shaft and is coupled by a hose to the discharge chute for creating an air flow in the chute downstream of the outlet which acts to draw and carry the chips along and into the collection bin. While such external fan devices are effective at entraining the chips, there is not always room enough on the chipper apparatus to accommodate the mounting of the external fan assembly. Further, the necessity of an additional air hose from the fan to the discharge chamber detracts from the appearance of the chipper apparatus, is prone to damage, and adds to the maintenance and cost of the apparatus.
One particularly effective drum-type wood chipper is fitted with a discharge fan internal to the housing of the chipping chamber, but isolated from this chamber by a circumferentially extending chamber wall. Air is drawn into the fan chamber through an inlet communicating with the air outside the chipping apparatus and discharged at a high velocity through an outlet of the fan chamber. A baffle separates the outlet of the fan chamber from a discharge area for the material being chipped in the drum. Air entering an exit chute from the fan chamber joins a flow of chips from the chipper and entrains the chips to carry them out of the material exit chute. The baffle prevents the stream of air from the fan chamber from flowing back into the chipping chamber. Although a marked improvement, this design does not overcome the problems of “blowback” from the drum chamber. Blowback occurs when the spinning of the chipper drum in the chipping chamber forces air out in all directions thus blowing air, chips and dust out the material infeed toward the operator.